448 



NA TURE 



\_Marck lo, 1887 



action lias actually extended so far as to neutralise that part of 

 the continuous lime spectrum having the same refrangibility as 

 the Gj8 line, the result being a black Sjiace in the .'-pectrum. In 

 the phosphoroscope the line of Gt is visible at the lowest speed ; 

 05 comes in at an interval of 0'0335 second, and the Ga line 

 immediately afterwards. 



Zm^/ sulphate, by itself, in the radiant-matter tube glows with 

 a nearly white colour, giving a continuous spectrum. In the 

 Iihosphoroscope the red and orange are cut off, leaving a strong 

 concentration of light in the green and blue. 5 per cent, of 

 lead added to calcium sulphate phosphoresces like lime. 



Magnesia phosphoresces pink. 5 per cent, with lime, as 

 sulphates, give a greenish phosphorescence, with a tendency to 

 turn red as the powder heats. The Oriental ruby containing 

 about between i and 2 per cent, of magnesia, a mixture was 

 prepared of acetate of alumina with 2 per cent, of magnesia, 

 and tested after ignition. It gave no spectrum or lines.' This 

 was done to see if the crimson line of aluminium might be due 

 to the presence of magnesia. 



Nickel added to calcium sulphate in the proportion of 5 per 

 cent, makes no alteration in the usual phosphorescent phenomena 

 of calcium. 



Potassium, 5 per cent., added to calcium sulphate gives a 

 bright phosphorescence, and made the residual glow very 

 persistent. 



Samarium. —The phosphorescent behaviour of this body, 

 alone and mixed with other substances, has been fully described 

 in my paper on samarium (Phil. Trans., 1885, Part II., pp. 

 709-21.) 



Scandium, either in the form of earth or sulphate, phosphor- 

 esces of a very faint blue colour, but the light is too feeble to 

 enable a spectrum to be seen. Addition of lime does not bring 

 out any lines. 



^ Sodium sulphate mixed with an excess of calcium sulphate 

 gives a greenish tinge to the usual colour of the phosphorescence. 

 The sodium line is visible in the spectrum. 



Slroitlia in the radiant-matter tube glows with a rich blue 

 colour, showing in the spectroscope a continuous spectrum with 

 a great concentration of light in the blue and violet. In the 

 phosphoroscope the colour of the glow is bright green, showing 

 in the spectroscope a continuous spectrum, with the red and blue 

 ends cut off. A mixture of calcium sulphate with 5 per cent, of 

 strontium sulphate behaves like calcium sulphate alone. 



Thorium, as oxide or sulphate, refuses to phosphorc-ce, and the 

 tube rapidly becomes non-conducting. A tube with thoria at one 

 end and a phosphorescent earth such as lime or ytrria at the other 

 end, and furnished with a pair of poles near each end, at a 

 particular exhaustion is non-conducting at the thorii end, while 

 it conducts at the yttria end. If the wires of the induction coil 

 are attached to the poles at the thoria end, no current will pass ; 

 rather than pass through the tube, the spark prefers to strike 

 across the spark gauge — a striking distance of 37 mm. — sho« ing 

 an electromotive force of 34,040 volts. Without doing anything 

 to affect the degree of exhaustion, on transferring the wires of the 

 induction coil from the thoria to the yttria end, the spark passes 

 at once. To balance the spark in air the wires of the gauge 

 must be made to approach till they are only 7 mm. apart, 

 equivalent to an electromotive force of 6440 volts ; the fact of 

 whether thoria or yttria is under the poles making a difterence of 

 27,600 volts in the conductivity of the tube. The explanation of 

 this action of thoria is not yet quite clear. From the great 

 difference in the phosphorescence of the two earths, it is evident 

 that the passage of the electricity through these tubes is not so 

 much dependent on the degree of exhaustion as upon the phos- 

 phorogenic property of the body opposite the poles. This view 

 is supported by the fact that the thoria may be replaced by a 

 metal wire, when the same obstructive action will result. 



Lime does not give phosphorescent properties to thoria, if this 

 earth be pure, but it brings out the lines of yttrium and samarium 

 which are almost always present in small qnantities in thoria 

 unless it has been specially purified. 



Tin with 95 per cent, of lime gives the lime phosphorescence 

 only. 



Thulium and erbium together phosphoresce with a green light, 

 giving the erbium spectrum already described before this Society 

 {Roy. Soc. Proc. vol. xl. p. 77, Fig. I, January 7, i8S6). There 

 is, in addition, a faint blue line app.irently double (see 

 "Ytterbium"). The addition of lime causes the mixtui'e to 

 phosphoresce of a pale blue colour. The spectrum now shows a 

 bright blue band, in the same position as the faint double blue 



band seen in the absence of lime. The blue line of Ga is also 

 seen, and a faint line of G5. The red line of Gtj, one of the 

 constituents of the ordinary yttria spectrum, is prominent in this 

 sjiectrum. 



TuugsUn and uranium, each mixed with 95 per cent, of lime, 

 only give the lime spectrum. 



Ytterbium. — I have not yet succeeded in preparing this body 

 of trustworthy purity; but'through the kindness of Prof. Cleve, 

 M. de Marignac, and Prof. Nilson, I have been enabled to 

 experiment with specimens of yttcrbia prepared by these chemists. 

 Prof. Cleve's ytterbia, in the form of sulphate, gives in- the 

 radiant-matter tube a blue phosphorescence, the spectrum of 

 which shows a strong double blue band,' together with traces of 

 the G5 and the erbia green lines. The addition of lime broadens 

 the blue band and makes it single. Prof. Cleve writes that this 

 ytterbia may contain some traces of thulia, perhaps also of erbia, 

 but scarcely any other impurities. Measurements in the spectro- 

 scope give the following approximate results : — 



The following are measurements taken with the mixture of this 

 ytterbia and lime : — 



These blue b.inds are seen much fainter without lime, and are 

 about as strong in the mixture of thulia and erbia with lime 

 described above. I had ascribed them to ytterbia, when Prof. 

 Nilson kindly forwarded me a small specimen of ytterbia, con- 

 sidered by him perfectly pure, and used for his atomic weight 

 determinations. This ytterbia gives absolutely no blue bands. 

 The origin of these bands therefore remains uncertain. 



Ytterbia from Prof. Nilson, in the form of sulphite, refuses 

 to phosphoresce without the addition of lime. When lime is 

 added it only brings out traces of the phosphorescent bands of 

 Ge, G/3, and Ga. Evidently these are impurities. 



Ytterbia from M. de Marignac is identical with that from M. 

 Cleve, as far as my examination can go. In sending me this 

 ytterbia M. de Marignac warned me that he was very far from 

 thinking it pure. 



Yttrium. — During the fractionation of the higher fractions of 

 yttria ( + 6, iiS and 119), a very sharp green line sometimes 

 makes its appearance, situated between G5 and G7 (approximate 

 position on the \j\^ scale, 325). It is very faint, and is not 

 connected with the orange line of SS, although it is as sharp. 

 The yttria showing these lines phosphoresces of a transparent 

 golden-yellow colour, the fractions at the other end phos- 

 phorescing yellowish green. 



I have previously described the action of a large number of 



(Roy. So, 

 ytterbia . 



; the band spoken of in my Royal Society paper of June 9 last 

 Proc. vol. xl. 1S86, p. 507), provisionally called 87, and ascribed to 



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